The Internet Protocol Multimedia Subsystem (“IMS”) is an architectural framework for delivering Internet Protocol (“IP”) multimedia to mobile users, such as users of smart phones or tablet computers. An IMS core network (“IMS core”) permits wireless and wireline devices to access multimedia, messaging, and voice applications and services. IMS standards and specifications have been promulgated by the 3rd Generation Partnership Project (“3GPP”).
To allow the IMS core to be integrated with Internet resources, the 3GPP specifications use Internet Engineering Task Force protocols within the IMS core, such as Session Initiation Protocol (“SIP”) and Diameter. SIP is a signaling protocol used for creating, modifying and terminating two-party or multiparty sessions consisting of one or several media streams. A mobile device registers its IP address with a SIP registrar server within an IMS core by generating and sending a SIP request message with a “REGISTER” method token. Once registered, a mobile device may subsequently establish multimedia sessions via the IMS core.
Some cellular phones are capable of allowing the user of the cellular phone to use multiple phone numbers. For example, some phones are capable of using multiple subscriber identity module (SIM) cards. A cellular phone with multiple SIM cards can receive and dial out from multiple phone lines as if the device were multiple devices. In other examples, some cellular networks or other entities provide applications (or “apps”) that allow the user to utilize multiple phone numbers.